How does DDOS work?

I am considering litespeed for its DDOS abilities but am having trouble finding a lot of details.

I read the recent article about how litespeed was used to stop a DDOS attack (http://blog.litespeedtech.com/articles/category/anti-ddos/) and wanted some more information on one sentence:
"LiteSpeed is able to detect the IPs (bot) that abuse servers and drop all the connections from detected bots"